Million Dollar Spaghetti

Name: Million Dollar Spaghetti
Ingredients: Two 24-ounce jars marinara sauce; 1 pound spaghetti; 1 tablespoon unsalted butter; 1 tablespoon olive oil; 8 ounces ground beef; 8 ounces sweet Italian sausage; 3 cloves garlic, minced; 1 medium yellow onion, diced; Kosher salt and freshly ground black pepper; 16 ounces ricotta (about 2 cups), at room temperature; 8 ounces cream cheese, at room temperature; 1/2 cup grated Parmesan (about 2 ounces), plus more for sprinkling; 1/4 cup chopped fresh parsley, plus more for serving; 1 large egg, at room temperature; 2 cups shredded mozzarella (about 8 ounces)